GB/T 29712-2023 Non-destructive testing of welds - Ultrasonic testing - Acceptance levels
1 Scope
This document specifies two ultrasonic acceptance levels known as acceptance level 2 (AL 2) and acceptance level 3 (AL 3) for full penetration welded joints in ferritic steels, which correspond to ISO 5817:2014, quality levels B and C. An acceptance level corresponding to ISO 5817:2014, quality level D is not included in this document, as ultrasonic testing is generally not requested for this weld quality.
These acceptance levels are applicable to testing carried out in accordance with ISO 17640.
This document applies to the testing of full penetration ferritic steel welds, with thicknesses from 8 mm to 100 mm. It can also be used for other types of welds, materials and thicknesses, provided the tests have been performed with necessary consideration of the geometry and acoustic properties of the component, and an adequate sensitivity can be employed to enable the acceptance levels of this document to be applied. The nominal frequency of probes used in this document is between 2 MHz and 5 MHz, unless attenuation or requirements for higher resolution call for other frequencies. It is important to consider the use of these acceptance levels in conjunction with frequencies outside this range carefully.
2 Normative references
The following documents are referred to in the text in such a way that some or all of their content constitutes requirements of this document. For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies.
ISO 5577 Non-destructive testing - Ultrasonic testing - Vocabulary
Note: GB/T 12604.1-2020, Non-destructive testing - Terminology - Ultrasonic testing (ISO 5577:2017, MOD)
ISO 5817:2014 Welding - Fusion-welded joints in steel, nickel, titanium and their alloys (beam welding excluded) - Quality levels for imperfections
ISO 17635 Non-destructive testing of welds - General rules for metallic materials
Note: GB/T 34628-2017, Non-destructive testing of welds - General rules for metallic materials (ISO 17635:2016, IDT)
ISO 17640 Non-destructive testing of welds - Ultrasonic testing - Techniques, testing levels, and assessment
Note: GB/T 11345-2023, Non-destructive testing of welds - Ultrasonic testing - Techniques, testing levels, and assessment (ISO 17640:2018, IDT)
ISO 23279 Non-destructive testing of welds - Ultrasonic testing - Characterization of discontinuities in welds
Note: GB/T 29711-2023, Non-destructive testing of welds - Ultrasonic testing - Characterization of discontinuities in welds (ISO 23279:2017, IDT)
3 Terms and definitions
For the purposes of this document, the terms and definitions given in ISO 5577 apply.
4 Determination of discontinuity length
The length of a discontinuity shall be determined by measuring the distance along the length over which the echo amplitude is above the evaluation level, using the fixed-amplitude level technique specified in Annex B.
5 Sensitivity setting and levels
The sensitivity setting shall be performed by one of the following techniques. For sensitivity setting and the subsequent testing, the same technique shall be used.
a) Technique 1: based on 3 mm diameter side-drilled holes.
b) Technique 2: based on distance-gain-size (DGS) curves for flat-bottomed holes (disk-shaped reflectors).
c) Technique 3: using a distance-amplitude-corrected (DAC) curve of a rectangular notch of 1 mm depth and 1 mm width.
d) Technique 4: using the tandem technique with reference to a 6 mm diameter flat-bottomed hole (disk-shaped reflector).
Four levels as defined in ISO 17640 are to be used:
a) reference level;
b) acceptance levels (for two quality levels);
c) recording levels (recording levels are 4 dB below the corresponding acceptance levels);
d) evaluation level.
All levels are linked to the reference reflectors specified in Table A.1 of Annex A.
The sensitivity setting techniques and corresponding levels shall be in accordance with Annex A.
Note: Reference grade is also called reference level; acceptance grade is also called acceptance level; record grade is also called record level; assessment grade is also called assessment level.
6 Acceptance levels
6.1 General
The relationship between acceptance levels, testing levels and quality levels is given in ISO 17635. See also Table 1.
The acceptance levels in this document are valid for all testing levels and for all techniques as defined in ISO 17640, including tests with straight-beam probes.
If characterization has been specified in accordance with ISO 23279, planar discontinuities are not acceptable and for non-planar discontinuities, the acceptance levels in this document apply.
If characterization has not been specified, the acceptance levels in this document apply to all discontinuities.
6.2 Indications from longitudinal discontinuities
Table A.1 gives information on the techniques used for evaluation of discontinuities according to ISO 17640 and the related evaluation and acceptance levels. Table A.2 specifies the reference levels for acceptance levels 2 and 3 for technique 2 using angle-beam scanning with transverse waves. Table A.3 specifies the reference levels for acceptance levels 2 and 3 for technique 2 using straight-beam scanning with longitudinal waves.
For techniques 1 (side-drilled holes) and 3 (rectangular notch), see Figures A.1 to A.4.
For techniques 2 [flat-bottomed holes (disk-shaped reflectors)] and 4 (tandem technique), see Figures A.5 to A.10.
Any discontinuities providing an amplitude below the acceptance level but with a length (above evaluation level) exceeding the following:
a) thickness t for the range 8 mm ≤ t ≤ 15 mm;
b) t/2 or 20 mm, whichever is larger, for all other thickness ranges.
It shall be subject to further testing. This requires the use of additional beam angle(s), and, if specified, the tandem technique.
The final evaluation shall be based on the maximum echo amplitude and length measured.
6.3 Indications from transverse discontinuities
When detection of transverse discontinuities is specified, the acceptance levels stated in 6.2 apply.
6.4 Grouping of discontinuities
Grouping of discontinuities is based on the length and the separation of individually acceptable discontinuities providing amplitudes above the recording level. The length of a group shall not be used for further grouping.
For evaluation, a group of discontinuities shall be considered as a single one if:
a) the distance, dx , between two discontinuities is less than twice the length of the longer discontinuity (see Figure 1);
b) the distance, dy , between two discontinuities is less than half of the thickness but not more than 10 mm; and
c) the distance, dz , between two discontinuities is less than half of the thickness but not
more than 10 mm.
The combined length of the group of two discontinuities is l12 = l1 + l2 + dx (see Figure 2).
The combined length, l12, and the larger maximum amplitude of the two discontinuities shall then be assessed against the applicable acceptance levels given in Table A.1.
